File:Chertified crinoid head in limestone (Fort Payne Formation, Lower Mississippian; Lake Cumberland, Kentucky, USA) (50669942703).jpg
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Fossiliferous limestone from the Mississippian of Kentucky, USA. The Fort Payne Formation of southern Kentucky is richly fossiliferous and is dominated by crinoids. Crinoids ("sea lilies") are sessile, benthic, filter-feeding, marine invertebrates that were abundant in Paleozoic oceans. The group nearly went extinct at the Permian-Triassic mass extinction 251 million years ago. Crinoids are not common in modern oceans - they are usually deep-water forms now, but some shallow-water forms also exist today. A crinoid is essentially a starfish on a stick. The stick, or stem, lifts the organism to a moderately high tier above the seafloor, which is conducive to non-competitive filter feeding. The flower-like "head" of the crinoid consists of numerous cemented calcite plates that surround the digestive system and other soft parts. The arms are feather-like and are the structures that engage in filter-feeding. In the fossil record, crinoid stems are common, whereas crinoid heads are uncommon to rare, because they disaggregate quickly after death. Individual pieces of a crinoid stem are called columnals - they are usually somewhat shaped like poker chips. Each columnal is composed of a single crystal of calcite (CaCO3 - calcium carbonate). The specimen seen here is a cross-section through a camerate crinoid head in limestone. The crinoid head itself has been replaced by cryptocrystalline quartz (SiO2) - this fossil preservation style is called "silicification", or in this case "chertification". A crinoid researcher has identified the crinoid head as Alloprosallocrinus conicus. Classification: Animalia, Echinodermata, Crinoidea, Camerata, Monobathrida, Composcrinina, Batocrinidae Stratigraphy: Fort Payne Formation, Osagean Stage/Series, upper Lower Mississippian Locality: lakeside exposure at the western-most tip of Cave Springs Ridge, southwestern-most end of Wolf Creek arm of central Lake Cumberland, southeastern Russell County, southern Kentucky, USA |
| Date | |
| Source | Chertified crinoid head in limestone (Fort Payne Formation, Lower Mississippian; Lake Cumberland, Kentucky, USA) |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/50669942703. It was reviewed on 20 January 2022 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 00:13, 20 January 2022 | | 2,142 × 1,526 (2.5 MB) | SeichanGant (talk | contribs) | Transferred from Flickr via #flickr2commons |
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